Structural panels used in architectural and passenger-vehicle applications are commonly covered with a decorative laminate. Decorative laminates used in such applications are typically constructed from a first layer adhered to a second layer. The first layer includes an exterior surface that is exposed to occupants of the area enclosed by the structural panels and through which a decorative pattern is visible. Therefore, the laminate must have suitable aesthetic characteristics, and physical characteristics to be formed three-dimensionally and stand up against wear and abrasion, and to resist soiling and adherence of ink or paint graffiti. To prevent damage to the decorative pattern due to abrasive or corrosive cleaning materials or acts of vandalism such as graffiti, the decorative pattern is disposed internally of an outer exterior surface of the first layer. The first layer can include materials that form an exterior surface that can be cleaned and is resistant to cleaning compounds. Fluropolymers such as Tedlar® from DuPont are well known by those knowledgeable in the art of decorative transportation laminates for their suitability as a first layer. These materials of the prior art include high concentration of halogenated compounds and can emit toxic gasses and opaque smoke when burned which will not pass regulations in some countries for use in underground tunnels. Another type of decorative interior panel includes a fiber glass reinforcement layer for strength and fire resistance, but has the disadvantages of higher weight and gauge thickness, higher cost and difficulty of three-dimensional forming. Likewise, high pressure laminates such as Formica® may pass combustion related tests, but may not pass cleanability/anti-graffiti requirements and more importantly have limited usage due to their inability be formed in three dimensions and potential for cracking and scratching. Another example of prior art would be a laminate of Tedlar® on top of Lexan®. This option is not known to have passed the combustion tests and could be impractical to thermoform due to high temperatures required. Another alternative would be a polyetherimide such as GE's Ultem® product capped with Tedlar®. This combination possibly could pass the combustion and cleanability requirements but its costs are not economical, and extremely high forming temperatures do not allow it to be considered for most commercial rail interiors.
Inside passenger vehicles, rail cars, aircraft and other compartments or confined spaces, such decorative laminates applied to structural panels pose a safety risk in the event of a fire. A fire that engulfs a portion of the passenger vehicle can ignite conventional decorative laminates installed therein. Smoke emitted by a burning decorative laminate can obstruct the visibility within the passenger vehicle and make evacuation difficult.
Similarly, conventional decorative laminates typically include materials that can emit toxic gases when burned. Various agencies around the world have promulgated regulations that establish threshold amounts of these toxins that humans can be exposed to for a predetermined period of time without exhibiting significant adverse effects. Decorative laminates containing materials that emit toxins in amounts above the threshold limits of such regulations when burned are unsafe for use in passenger vehicles and other confined spaces that may be occupied by humans.
Accordingly, there is a need in the art for a decorative laminate that can be used within passenger vehicles as well as other confined spaces, which produces minimal amounts of smoke and toxic gases when burned, has a low burning rate, is readily cleanable (i.e., resistant to permanent staining), and has resistance to degradation by topically applied cleaning agents and abrasive materials.
It has been difficult in the industry to achieve decorative laminates having both suitable toxicity and flammability characteristics, while providing a durable decorative surface with color stability, and chemical resistance to stains and cleaning agents. While fire retarding additives lower the amount of heat release and flame spread, they also can produce additional smoke and toxic gases. Also fluoropolymers are well known to be durable, chemical and stain resistant cap films. Unfortunately, the Fluorine in these fluoropolymers produce additional toxic gases when burned. Adding other factors such as cost, weight, ease of handling, and formability, make the achievement of meeting all fire, smoke, toxicity and cleanability requirements a challenge.